The broad goal of this research is to examine the impact of managed care on the demand and supply of primary care and specialist physician services and their practice organization. The specific aims are to use existing data for the period 1984-1995 to examine the extent to which the level of managed care penetration in geographic markets for physician services affects patterns of compensation, location and use of primary care and specialist physicians. It is hypothesized that in markets with higher levels of managed care penetration: 1) The incomes and hourly compensation of primary care physicians are higher relative to specialty physicians. 2) The ratio of primary care to specialist physicians is higher. 3) The absolute number of primary care physicians per capita is higher and the absolute number of specialist physicians per capita is lower. 4) Specialists perform more primary care activities and work fewer hours. Hypotheses will be tested at the market level and, alternatively, using the individual physician as the unit of analysis. Market-level analysis will be performed at two levels, states and MSAs, and will use pooled cross-sectional time series data to estimate reduced form fixed effects and "changes in changes" models. Physician level analysis will also be performed to test hypothesis regarding the impact of managed care on individual physician income, hours and activities, accounting for physician-specific demographic, educational and practice-related characteristics. Physician-level data will be drawn from the American Medical Association Socioeconomic Monitoring System (SMS) surveys for 1984-1995. SMS data will be used to construct measures of managed care penetration at the state and MSA level based on the percentage of physician revenues draw from managed care contracts. These measures will be compared to existing alternative measures of managed care penetration based on HMO enrollment data and market surveys of insurance coverage.